Granular propellant containing kno{11 {11 and unsaturated ester

ABSTRACT

A propellant of improved ballistic efficiency for small arms ammunition comprising potassium nitrate and, as surface moderant, a non-saturated ester having at least two ester groups and at least two -C C- groups in its molecule.

United States Patent 1 1 Wood Dec. 4, 1973 GRANULAR PROPELLANT CONTAINING KNO AND UNSATURATED ESTER [56] References Cited [75] Inventor: Herbert Leslie Wood, West UNITED STATES PATENTS Kilbridge, Scotland 3,520,742 7 1970 Witz 149/19 x 3 539 377 11/1970 Steinle 149/7 X [73] Asslgneez Imperial Chemical Industries,

1 Limited o o E g a 3,551,222 12/1970 Kaufman et a1. 149/61 X [22] Filed: Nov. 9, 1972 Primary Examiner-Leland A. Sebastian [2]] Appl No: 304,948 Attorney-Cushman, Darby & Cushman 30 F A u ti P 1 D [57] ABSTRACT I orelgn pp ca y am A propellant of improved ballistic efficiency for small NOV. 23, Great Blltaln a arnmunition comprising potassium n a a surface moderant, a non-saturated ester having at least [52] US. Cl. 149/7, 149/19, 149/61, two ester groups and at least two groups in 149,100 264/3 B its molecule. [51] Int. Cl. C0611 19/02 [58] Field of Search 1. 149/7, 61, 19, 100 12 C N Drawings 1 GRANULARPRQPEPPANT Q W I KNOQ AND UNSATURATED ESTER This invention relates to a surface moderated granular propellant suitable for small arms ammunition and to a method of preparing such propellant.

Granular propellants for small arms are usually based on nitrocellulose, and may contain, in addition to nitrocellulose, other energetic constituents, stabilisers, glazing agents and such common ingredients. They also usually contain a surface moderant applied to the surface of the grains, the moderant being in greater contion towards the interior of the grain.

The surface moderants usually employed include methyl centralite (sym-dimethyl diphenyl urea), ethyl centralite, dibutyl phthalate and dinitrotoluene. It is also usual for the propellant to contain a potassium salt, for example, potassium sulphate, to suppress muzzle flash.

We have now found that the ballistic efficiency of surface moderated propellant can be improved by incorporating potassium nitrate in the base propellant and including, as the surface moderant, an unsaturated ester having at least two ester groups and at least two C=C groups in its molecule. The use of these unsaturated esters in propellants not containing potassium nitrate gives a slight increase in bulk density but no improvement in ballistic efficiency. The incorporation ofpotassium nitrate into propellants coated with conventional surface moderant, for example methyl centralite, gives a small increase in ballistic efficiency but the effect is offset by a reduction in bulk density which restricts the amount of propellant which can be loaded into a given cartridge. The use of potassium nitrate in combination with the unsaturated esters as surface moderants gives increased ballistic efficiency without reducing the density so that the increased efficiency can be realised as an improvement in ballistic performance. In the present context, ballistic efficiency means the ratio of the kinetic energy of the projectile to the propellant charge weight.

Thus, in accordance with this invention, a surface 'centratio'n'at the surface and diminishing inconcentra= moderated granular propellant contains potassium nitrate and, as a surface moderant, an unsaturated ester having at least two ester groups and at least two C=C- groups in its molecule.

Preferred esters are those having eight to 20 carbon atoms and preferably they are derived from an alcohol having two to 10 carbon atoms and an acid having three to 10 carbon atoms. The C=C groups may be derived either from the alcohol or acid (or both) precursors of the ester.

The ester may, for example, be derived from a polyhydric alcohol and an unsaturated carboxylic acid or from an unsaturated monohydric alcohol and a polybasiccarboxylic acid. Convenient polyhydric alcohols include ethylene glycol, triethylene glycol, tetraethylene glycol, hexamethylene glycol, decamethylene glycol,

tripropylene glycol and pentaerythritol. A convenient unsaturated monohydric alcohol is allyl alcohol. Convenient unsaturated monobasic carboxylic acids include acrylic acid and methacrylic acid and convenient dibasic acids include fumaric acid, maleic acid, itaconic acid and sebacic acid.

Preferred unsaturated esters include ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, decamethylene glycol dimethacrylate, hexamethylene glycol diacrylate, tripropylene glycol diacrylate, pentaerythritol tetraacrylate, diallyl sebacate, diallyl fumarate, diallyl maleate and diallyl itaconate. Of these esters triethylene glycol dimethacrylate is preferred as it is readily obtainable in stable form, has low vapour pressure and is easy to apply to the propellant grains.

The unsaturated ester preferably constitutes l to 4 percent by weight of the total propellant composition and the potassium nitrate preferably constitutes 0.4 to 1.6 percent by weight of the total composition.

The invention also includes a method of preparing a surface moderated propellant wherein an unsaturated ester having at least two ester groups and at least two C=C groups in its molecule is applied as a surface moderant to granular propellant containing potassium nitrate.

From a further aspect the invention consists in a method of improving the ballistic efficiency of granular propellant which method comprises incorporating potassium nitrate into a granular propellant composition and applying to the propellant, as a surface moderant, an unsaturated ester having at least two ester groups and at least two C=C groups in its molecule.

The surface moderant may be applied in solution to the surface of the propellant grains but we have found that the concentrated moderant can be advantageously used. Penetration of the moderant into the interior of the propellant grains is effected by heating and the heat may advantageously be supplied by injecting steam or mixing hot water with the grains. In a preferred procedure the moderant and grains are mixed by stirring or tumbling, and heated by injection of steam followed by steeping in hot water at 60 to C and drying. This water treatment leaches out part of the potassium nitrate originally present in the propellant grains and, if a high potassium content is required in the final surface moderated grain, for example to reduce muzzle flash, a water insoluble potassium compound, for example potassium aluminium fluoride, may be advantageously added to the base composition.

The improved ballistic efficiency of the surface moderated propellants of the invention compared to surface moderated propellants of the prior art can be realised by varying the quantity of the surface moderant to obtain an increase in projectile velocity for a given powder charge and firing chamber pressure, a reduced charge weight required for a given projectile velocity at a given chamber pressure or a reduced chamber pressure for a given charge weight producing a given projectile velocity.

These propellants are as good in all other respects as surface moderated propellants of the prior art, for example, in bulk density, ballistic stability, ignitability, and high and sub-zero temperature performance.

The beneficial effects obtainable by the invention are most marked with single-base propellants, i.e. those based on nitrocellulose without any other self-explosive constituent.

The ballistic efficiency is not directly related to the moderating effectiveness of the surface moderant and in order to achieve the improvement in ballistic efficiency it may be necessary to use a somewhat higher weight proportion of moderant than was used in compositions of the prior art. The higher proportion of moderant is beneficial in that it reduces the heat of explosion and reduces barrel erosion.

The invention is further illustrated by the following Examples wherein all parts and percentages are given ted through a piston. From a series of tests the charge weight of each powder (and also the convenient proportion of surface moderant) to give a mean maximum chamber pressure of 20 tons/square inch was deterby weight. 5 mined and the velocity of the bullet using this charge Examples 1, 2 and 3 are not in accordance with the weight was measured by recording the time for the bulinvention and are given for comparison. let to pass between photoelectric detectors placed respectively at 3 and 12 metres from the muzzle of the EXAMPLES barrel.

In preparing the propellant powders of the example, The ballistic efficiencies in Table 2 are related to the propellant dough was prepared from the ingredients inprior art powder of Example 1. It is evident from these dicated in Table l and the dough was formed into tuburesults that the surface moderatedpowders made in aclar grains by extrusion through a die of internal diamecordance with this invention using unsaturated esters as ter 1.27 mm provided with a central pin of diameter surface moderants have higher ballistic efficiencies 0.35 mm, and cutting to lengths of 1.27 mm. The so l- 15 than the prior art powders.

FARE? 2 Relative Charge Mean ballistic Residual Residual Residual weight velocity efficiency KN O; K2A1F5 K2804 (grams) (ft/sec.) V Q Example Surface moderant parts added/100 parts base grain (percent) (percent) (percent) (Q) (V W Methyl centralite 1.000 3.5 do 2. 1.022 Triethylene glycol dimethaerylate. 0. 973 do 1.052 o 2.65 1.041 Tetraethylene glycol dimethaerylare... 2. 78 743 1. 043 3.0 Ethylene glycol dimethacrylate 2.60 2, 672 1. 059 3. 4 Hcxamethylene glycol diacrylate. 2. 75 2, 731 1. 044 3.0 Decamethylene glycol dimethacrylat 2.70 2,708 1.046 3.0 Tripropylene glycol diacrylate 2.77 721 1.029 3.5 Penaterythritol tetra-acrylate... 2.56 2 1,035 3.5 Diallyl maleate 2. 65 6 1. 062 3.0 Diallyl sebacate 2. 76 725 1. 037 .75 Diallylfumarate 2.64 678 1.044 3.5 Diallylitaeonate 2.67 2 710 1.058

vent was removed by drying in an air blast. The tubular grains thus formed (base grain) had an annulus thickness of approximately 0.33 mm and an outside diameter of approximately 0.84 mm.

TABLE Base Grain Composition Examples Composition (before steeping) Examples 2, 4 and Example (parts 1 and 3 6 to 15 5 Nitrocellulose (13.2% N) 225 225 225 Potassium nitrate 4.5 4.5 Potassium sulphate 3.0

Potassium aluminium fluoride 1.5 Diphenylamine 2.5 2.5 2.5 Ether 150 150 150 Ethanol 100 100 100 100 parts of the base grain were tumbled in a rotating pan with 17 parts of water and 0.3 parts of graphite for five minutes and the surface moderant as indicated in Table 2 was added. Steam was injected into the pan for 45 minutes, the temperature of the grain rising to 80C over 25 minutes and remaining thereat for 20 minutes. The grains were then steeped in 400 parts of hot water for 22 hours and dried to a moisture content of 1.3 percent.

Results of tests on the surface moderated propellants of the Examples are given in Table 2. In testing the ballistic properties the propellant powders were loaded into 7.62 millimetre calibre ammunition, having necked brass cases and 9.3 gram bullets, and tired in a standard proof barrel. The chamber pressure was measured at a distance of 2.2 centimetres from the breech by a radial pressure gauge wherein the pressure was indicated by the deformation of a copper cylinder to which a thrust generated by the prrssure was transmit- What we claim is:

1. A surface moderated granular propellant containing potassium nitrate and, as a surface moderant, an unsaturated ester having at least two ester groups and at least two C=C groups in its molecule.

2. A propellant as claimed in claim 1 wherein the ester is one having eight to 20 carbon atoms and is derived from an alcohol having two to 10 carbon atoms and an acid having three to 10 carbon atoms.

3. A propellant as claimed in claim 1 wherein the ester is derived from a polyhydric alcohol and an unsaturated carboxylic acid.

4. A propellant as claimed in claim 1 wherein the ester is derived from an unsaturated monohydric alcohol and a polybasic carboxylic acid.

5. A propellant as claimed in claim 1 wherein the ester is an ester of a compound selected from the group consisting of ethylene glycol, triethylene glycol, tetraethylene glycol, hexamethylene glycol, decamethylene glycol, tripropylene glycol, pentaerythritol and allyl alcohol and a compound selected from the group consisting of acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid and sebacic acid.

6. A propellant as claimed in claim 1 wherein the ester comprises ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, decamethylene glycol dimethacrylate,

the total composition.

8. A propellant as claimed in claim 1 containing a water insoluble potassium compound.

9. A method of preparing a surface moderated propellant as claimed in claim 1 in which method an unsaturated ester having at least two ester groups and at least two -C=C- groups in its molecule is applied as a surface moderant to granular propellant containing potassium nitrate. 

2. A propellant as claimed in claim 1 wherein the ester is one having eight to 20 carbon atoms and is derived from an alcohol having two to 10 carbon atoms and an acid having three to 10 carbon atoms.
 3. A propellant as claimed in claim 1 wherein the ester is derived from a polyhydric alcohol and an unsaturated carboxylic acid.
 4. A propellant as claimed in claim 1 wherein the ester is derived from an unsaturated monohydric alcohol and a polybasic carboxylic acid.
 5. A propellant as claimed in claim 1 wherein the ester is an ester of a compound selected from the group consisting of ethylene glycol, triethylene glycol, tetraethylene glycol, hexamethylene glycol, decamethylene glycol, tripropylene glycol, pentaerythritol and allyl alcohol and a compound selected from the group consisting of acrylic acid, methacrylic acid, fumaric Acid, maleic acid, itaconic acid and sebacic acid.
 6. A propellant as claimed in claim 1 wherein the ester comprises ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, decamethylene glycol dimethacrylate, hexamethylene glycol diacrylate, tripropylene glycol diacrylate, pentaerythritol tetra-acrylate, diallyl sebacate, diallyl fumarate, diallyl maleate or diallyl itaconate.
 7. A propellant as claimed in claim 1 wherein the unsaturated ester constitutes 1 to 4 percent and the potassium nitrate constitutes 0.4 to 1.6 percent by weight of the total composition.
 8. A propellant as claimed in claim 1 containing a water insoluble potassium compound.
 9. A method of preparing a surface moderated propellant as claimed in claim 1 in which method an unsaturated ester having at least two ester groups and at least two -C C- groups in its molecule is applied as a surface moderant to granular propellant containing potassium nitrate.
 10. A method as claimed in claim 9 wherein the propellant is heated to effect penetration of the moderant into the interior of the grains.
 11. A method as claimed in claim 10 wherein the propellant is heated by steam or hot water.
 12. A method as claimed in claim 10 wherein the ester and the propellant grains are mixed and heated by steam injection followed by steeping in hot water at 60* to 70*C. 